Differential driving gearing



y 19, 1941 J. L. WILLIAMSQN 2,283,661

DIFFERENTIAL DRIVING GEARlNG Filed Nov. 20, 1940 3 Sheets-Sheet 1 ay 1 9 J. L. WILLIAMSON DIFFERENTIAL DRIVING GEARING 5 Sheets-Sheet 2 Filed Nov. 20, 1940 y 19, 1942- 4 J. L. WILLIAMSON 2,283,661

DIFFERENTIAL DRIVING GEARING Filed Nov. 20, 1940 3 Sheets-Sheet 5 Patented May 19, 1942 Eur OFFICE James L. Williamson, Springfield, Vt.,,assignor to- The Fellows Gear Shape: Company, Springiield,vt.,'acorporation of Vermont ApplicationNovemberZD, 1940, Serial No. 366,396

12 Claims.

- The present invention relates to driving gearing of the differential-type adapted to transmit rotation to a plurality of machine elements, such as shafts or wheels, at equal or unequal speeds.

Such gearings, are used in connection with the driving wheel axles of automobiles to transmit the propelling power while permitting a speed differential between the two driving road wheels in rounding curves and turning corners. The usual differential gear so usedhas the defect that, if one of the driving wheels bears on a slippery place where the traction is too poor to sustain the propelling thrust, it will cause such clution beyond the other sun gear;

wheel to spin and allow the other to remain stationary. This condition occurs, for instance, when an attempt is made to start an automobile while one of its driving wheels rests on an icy or similarly slippery spot in the road while the other rests on a surface having a greater coeiflcient of friction. In such circumstances the power applied by the engine rotates only the wheel of which the traction is insufficient to prevent slipping and the car does not start. I

Attempts have been made to overcome this drawback, including a bevel gear and pinion differential in which the planet pinions are mountilar resultsby other means which have certain manufacturing and operative advantages hereinafter described. Two of the forms in which the invention may be embodied are illustrated in the drawings, in which Fig. 1 is a horizontal section of a differential trating the positions of the gears when one sungear has been advanced through a quarter rev-v Fig. 5 is a diagram similar to Fig, 3 but illustrating a different manner of assemblage of the gears;

Figs. 6 and 7 are diagrams showing the principles of the invention in a differentibut equivalent, embodiment; I

Fig. 8 is a fragmentary sectional viewof a differential gearing having bevel gears embodying the same principles. Like reference characters designate the same parts wherever they occur in all the figures.

Assuming that the-illustration here given is that of the rear axle driving gearing of an automobile, the character ll represents the propeller shaft of the automobile which is driven by the engine through any suitable transmission means. A bevel pinion I! on shaft ll meshes with a bevel gear l3 which is mounted rotatably on shaft M which forms one of the alined sections of the rear axle to which the propelling road wheels of the automobile are secured. The other axle section is shown at l5. These axle sections carry gears l6 and I1, here shown as integral with them, but which may be otherwise rigidly secured to them. These gears'are herein referred to as sun gears becausethey runv in mesh with pinions having a planetary motion. Although the gears .here shown are unlike those more commonly understood by the term sun gears", in that they are neither surrounded by, nor surround, the orbit of their planet pinions, yet they are analogous in operation to such sun gears and may properly be so called for the purpose of de-' fining the present invention. Planet pinions .l8 aresupported between and in mesh with the sun gears l6 and I1, being mounted to rotate about their geometrical axes on pivots I9 of a pinion carrier 20. Such pinion carrier is located gearing containing such embodiment, and in.-

planet pinions are spur pinions;

which the sun gears are face gears and the 2 Fig, 2 is an elevation of the parts beyond the line 22 of Fig. 1 as viewed in the direction of the arrows on said line;

Fig. 3 isa diagram showing two of the planet pinions and a development into one plane of between the-contiguous ends of the axle sectionswith the pivots extending radially outward, all. in thefsame plane midway between the sun .g'e'ars. and the protruding ends of the pivots are held in. a casing-2| which is secured to the bevel gear 13 and encloses the differential gear assemblage. here shown, the casing 2| is 5 made'of two parts bolted together'on the axial the parts of the sun gear teeth intersected by-a cylinder of which the traces are indicated at 3-3 in Figs. 1 and 2;

plane of the pinion pivots, and having a flange 22 which is secured by bolts 23 to the gear l3. The teeth of each sun gear are all in a surface of revolution about the axis of the gear, and those of each pinion are equally distant from Fig. 4 is a diagram similar to Fig. 3 but illusthe axis of the pinion.

' The diiferential gearing thus illustrated diilers from the usual rear end driving mechanism for automobiles in that, either- (a) The teeth of either or both sun gears are spaced with repeated progressive elongations and contractions of circular pitch and all are conjugate to the planet pinions of uniform tooth spacing: or, alternatively,

(b) The teeth "*of the planet pinions have varying anglarspacing about their axes, while being conjugate to sun gear teeth of uniform spacing;

(c) Preferably, although not necessarily, the sun gears are face, or crown, gears and the planet pinions are spur gears.

The condition described in paragraph a above is illustrated diagrammatically in Figs. 3-5, wherein the teeth of the face gears shown in Figs. 1 and 2, at their intersections with a coaxial cylinder, passing through line 3-3 of Figs. 1 and 2, near the inner ends of the teeth, are represented as developed into the plane of the drawings. Considering first the gear l6, its teeth are arranged in recurring groups or series a, b, c, d, e, j, a, b, etc. to P, which is the last one of the circuit beginning with a and extending from left to right. The pitch spacing is at the widest between tooth a and teeth I and b at either side. It diminishes from b to c, and from c to d, by successive contractions, and then elongates from d to e, e to j and j to a. From a to b to c to d the spacing diminishes again; and this cycle of diminishing and increasing pitch distances is repeated throughout the circuit of the gear. There may be any number of teeth in one group or cycle of the character described,

and a single one, or any larger number, of such tiple (from one upward) of the number in one group.

The teeth of the planet gears or pinions l8 are all alike, all equidistant from the axes of the respective pinions and equally spaced around such axes. Such teeth, and those of the sun gear are mutually conjugate. Thus the sun gear teeth, owing to their variable spacing, differ from one another in pressure angle; those of wider spacipg having relatively large pressure angles and included angles between their side faces, and those of narrower spacing having relatively small pressure angles and included angles.

The teeth of sun gear I! are like those of gear l6, and are designated in the diagrams by the same reference letters modified by appropriate exponents. All teeth designated by the same reference letters, disregarding exponents, are alike in both gears and in all recurring groups of teeth in each gear.

The sun gears are assembled with the planet pinions in such manner that teeth of wider spacing of one sun gear will come into full mesh with the pinions when teeth of narrower spacing of the other sun gear mesh with the pinions at the diametrically opposite side of the latter. In most cases, although not universally, the teeth of I widest spacing and largest included angle of one est spacing of the other gear. This is the condition illustrated in Figs. 3 and 4.

In Fig. 3 the teeth a. a, a, etc..of gear IO, which are the teeth of maximum angle between their side faces, mesh with the planet pinions diametrically opposite to the teeth 11, d, d, etc., the teeth of the gear H which have the minimum included angle. The active pressure angle between the pinion and the gear I6 is shown at A and is .a maximum, while that between the pinion and the gear I1 is shown at B and is a minimum. The effective pitch point of the pinion with gear l8, designated :2, is at this time more distant from the axis C of the pinion than is the effective pitch point p of the pinion with the gear l1. Thus, if it be assumed that the pinion acts as a driver turning about a stationary axis, while the sun gears are free to rotate, the pinion tends to drive the gear I6 at maximum angular velocity and the gear I! at minimum angular velocity. But the effective leverage (pitch radius) constantly varies, increasing and diminishing, with respect to the gear l1, while gear are placed opposite those with the narrowit diminishes and then increases with respect to the gear l6, between values equal to Cp and Up as to each gear. a

The effect produced by such varying leverage when one road wheel slips by reason of poor traction and the other is held stationary by good traction is this: The planet pinions roll on the stationary sun gear and rotate the other sun gear with varying angular velocity. Assuming that the gear i1 is stationary and that the pinions roll with uniform translative velocity in the direction of the arrow D shown in Fig. 4, then the pinion l8 in rolling from full mesh with tooth d to full mesh with tooth a advances the gear l6 until the tooth d of that gear comes into full mesh with it. During this period the eilective pitch radius of the pinion with respect to gear H is lengthening, until it becomes equal to Cp,

and that with respect to gear I6 is shortening to,

the length Cp', whereby rotation of the pinion about its own axis is relatively retarded. and rotation of sun gear I6 is further retarded. In the further travel in the same direction, until the pinion meshes with the teeth d and a its pitch radius with respect to gear l'l becomes longer and that with respect to gear l8 shorter, and the rotational speed of gear I6 is accelerated. The other pinions coact in like manner with other similar teeth of the sun gears. Thus the spinning wheel is advanced with repeated relative retardations and accelerations. If the planet pinions are revolved in their orbit with acceleration enough to cancel the retardation of rotation about their own axes, the net result is a succession of accelerations of the spinning wheel. These are repeated as many times in each revolution of the pinions as the number of recurring groups or cycles of teeth in the sun gears. The accelerating impulses are delivered against the mass and inertia of the spinning wheel, the reaction of which, transmitted through the pinions, causes forward driving impulses to be applied to the stationary wheel. The latter impulses are added to the tractive effort of the spinning wheel, with propelling effect on the vehicle. The frequency and power of such propelling impulses increase in proportion to increase in the speed of the engine.

It should be noted that the invention is not limited to the principle of variable tooth spacing in both sun gears, but that it embraces the condition in. which the teeth of only one sun gear are thus variably spaced while those oi'the other are uniformly spaced. With the latter arrangement, results the same in kind are obtained as with that where both sun gears have variably spaced teeth, although the intensity, or degree,

of the impulses delivered to the spinning gear'is less. I

One of the advantages of the new combination herein described is that the number of planet pinions is independent of the gear ratio between iace gears'and pinions. The present illustration shows four pinions with a two to one ratio. But' there may be any number oi pinions, from one up to the number oisets or cycles of recurring teeth in the sun gears. The four pinions of the illustrative embodiment are set 90 apart around the axis of the sun gears. But there might be only one pinion; or two pinions spaced either 180 apart, or 90 apart in one direction around the .sun gear axis and 270 in the opposite direction;

pinions in a small gear ratio enables the pulsatangle occurs betweenteeth tand 1 Between.

t and t the angle is equalto that. between t and t between t and t the angle is equal to that between t and t and that between t and t is equal to that between i and it. Thus, proceeding either way around the axis C from the smallest angle, there-is a. progressive increase of tooth spacing to the opposite side of the pinion,

and then a progressive decrease to the starting point. The angles referred to are those between -.the median radial lines of the teeth, designated by dot and dash lines in-the drawings.

The thickness 01 the different teeth and their face curves are established in proper ratio to the angular spacing so as to cause coaction of the pinion teeth with the face gear teeth on lines of action all having the same inclination but crossing the sun gear teeth at difierent points between the roots. and crests of the latter. The lines of action between the pinion teeth t and t and any tooth or either sun gear, are shown at Va. and 1% respectively. The corresponding ing efiect previously described to be obtained with a good distribution and balancing of forces without making the assemblage unduly large.

Another advantage is that the sun gears may be assembled in any position, except exact opposition of like teeth of the sun-gears diametrically across the pinions, without causing any difficulty or sacrificing more than a portion of the desired impulse effect. This is made clear by Fig. 5, in which the pinions are related to the gear I! in the same manner as represented in Fig. 3, but the gear I6 is set over to the right by the distance of one tooth from the position shown in Fig. 3. Although the pitch radius G1: with respect to gear I6 is shorter than the pitch radius 017, it is longer than the pitch radius C11; and

lines of action of the teeth i and t are shown 'at Z 0. and 1111." respectively. All lines of action have the same inclination with respect to a lane perpendicular to the axis of the sun gears. It follows from these conditions that the pitch radius Cp between either tooth t or t and a sun gear tooth embraced between them is longer than the pitch radius Cp' on which the contiguous faces of the teeth t and t coact with a sun gear tooth. With respect to faces of the pinion teeth flanking other spaces, the lines of action and pitch points are at progressively varying disthroughout the cycle of operations there are differences of pitch radii between the pinions and the two gears of the same character as that previously described, but of less degree. Such an I arrangement may be desirable at times in order to soften the shocks due to recurring impulses applied to a spinning wheel.

The same effects are obtainable by a reversal of the arrangement previously described, in which the teeth of the pinion or pinions are variably spaced while the teeth of the sun gears are equally spaced and are identical with one another as to form and pressure angle. Such an alternative embodiment is diagrammatically illustrated in Figs. 6 and 7, where the sun gears are designated l6l. and Hi, and one of the planet pinions is shown and designated l8l. The pinion rotatesabout. its geometrical axis C, which is located midway between the sun gears, as in the previous illustration, but the teeth of the pinion are spaced with variable angular spacing about the axis C while being equidistant therefrom. Between teeth t and t is the smallest angle; between if and t a larger angle, which is equal to that between t and t between t and t astill larger angle; and the angles between successive teeth are progressively larger, until the largest tances from the axis C between the limits designated by the lines and points here shown.

Thus if the gear I'll be considered as stationary and gear lBi free to rotate, while the pinion is carried in a planetary path, then, in rolling from the position shown inFig. 6 to that shown in Fig. 7, the pinion will coact with the stationary sun gear I'll on progressively lengthening pitch radii, and with the spinning sun gear on .progressively diminishing radii. During the further progression until a relationship like that shown in Fig..6 is reached, an acceleration is imparted to the spinning sun gear. Thus the efiect is the same as in the case precedently described. In the second case there is-no limit, except space and strength limitations, to the number of planet pinions which can be used in the assemblage, or to the gear ratio and number of teeth of sun and planet gears. Nor is there any limitation as to angularspacing of the pinions around the axis of the sun gears. It is only necessary that corresponding teeth of all the pinions be meshed with the sun gears at the same time. The sun gears may be assembled in any position of angular rotation about their axis with respect to the pinions, since all of their teeth are alike.

The principles and advantages of this invention are not conditioned on the use of face'gears 1, but differing only in that the sun gears Mia and Ila.- are bevel gears and the planet pinions I8a are likewise beveled. This latter illustration typifies tapered ,gears also, i. e. those which are generated by a gear shaper cutter recipro eating on anjaxisinclined to the, axis of the pinion, and complementally inclined to the axis or as excluding any other uses to which it may be applied; except as to such claims as may be definitely limited by their context to a specific use.

What I claim and desire to secure by Letters Patent is:

1. A differential gearing comprising sun gears, each having teeth on one face, mounted coaxially and rotatably with their toothed faces opposite to, and spaced apart from, one another, and a planet pinion supported to rotate about its geometrical axis and to revolve about the axis of the sun gears between, and in mesh with the teeth of, both said sun gears, the teeth of said gears and pinion being relatively unequally spaced with progressively increasing and decreasing spacing so as to cause alternate accelerations and decelerations of the sun gears when the planet pinion is held in one location and rotated at uniform speed about its own axis as a driver.

2. A differential gearing for applying recurrent impulses to a rotatable part of the gearing when another part is withheld from rotation, comprising two sun gears mounted rotatably face to face with a space between them, a planet gear mounted in said space to revolve about the axes of the sun gears and to rotate about its own axis, and means for so revolving said planet gear; said planet and sun gears having conjugate intermeshing teeth, of which the teeth of one of said gears are equally spaced on a circle coaxial with that gear, and the teeth of the intermeshing gear are variably spaced on a circle coaxial with such intermeshing gear, with progressive- 1y increasing and then progressively decreasing distances between successive teeth.

3. A differential gearing consisting of coaxial opposed sun gears and a planet pinion between and in mesh with said sun gears supported to revolve around the axis thereof, in which the teeth of the sun gears are variably spaced while being conjugate to the planet pinion, or vice versa, such variable spacing comprising progressive increases of distance between successive teeth followed by progressive decreases of distance between a further succession of teeth.

4. A differential gearing for transmitting i torque to two rotatable members and applying recurrent impulses to one of said members when the other is withheld from rotation, comprising two sun gears mounted rotatably face to face with a space between them, each provided with teeth on the face thereof which is turned toward the other sun gear, a planet pinion mount-- ed in said space and having peripheral teeth conjugate to and in mesh with the teeth of said sun gears, a carrier on which said planet gear is mounted to rotate about an axis coaxial with its peripheral teeth, said carrier being mounted to rotate about the axes of the sun gears, and means for rotating the planet gear carrier about said axis and thereby revolving the planet gear, the teeth of one of said sun gears being variably spaced with progressive incnea'ses of distance be tween successive teeth followed by progressive decreases of distance between a further succession of teeth.

5.:A differential driving gearing comprising sun gears coaxially mounted for rotation with a space between them and having teeth on their contiguous faces, a pinion carrier mounted to rotate around the axis of said sun gears, means for imparting rotation to said pinion carrier, and a planet pinion mounted rotatably on said pinion carrier with its teeth in mesh with both sun gears, the teeth of said planet pinion being at equal distances from the axis of the pinion and the teeth of the sun gears being spaced with progressive increases and decreases ofcircular pitch, in a manner to cause alternate relative accelerations and retardations of either sun gear when the other sun gear is held stationary and the pinion is carried planetwise at constant speed around the axis of the sun gears.

6. A differential gearing comprising two sun gears each having teeth on one face mounted coaxially and rotatably with their toothed faces opposite to, and spaced apart from, one another, a planet gear having peripheral teeth equidistaut from its axis, and means supporting said planet gear in mesh with both sun gears to rotate about its own axis and revolve about the axis of the sun gears, the teeth of said planet gear being unequally spaced around the axis thereof with progressive increases of angular spacing as to a succession of teeth and progressive decreases of such spacing as to a further succession of teeth; and the teeth of the sun gears being equally spaced on a circle coaxial with the sun gears.

7. A differential gearing comprising sun gears each having teeth on an end face rotatably mounted with their axes in alinement and their toothed faces toward one another with a space between them, a pinion carrier mounted to rotate about the axis of said gears, a plurality of planet pinions mounted on said carrier in positions enabling them to travel in an orbit around said axis when the carrier is rotated, and to rotate about their respective axes transverse to such orbit, and means for rotating said carrier; the teeth of the several pinions being equidistant from and spaced equiangularly around their respective axes and the teeth of the face gears being conjugate to those of the pinions and being arranged in a plurality of groups, each containing the same number of teeth and in which the teeth are spaced with symmetrical and progressive increases and decreases of distance between them; the angular disposition of the planet pinions around the axis of the face gears being equal to the angle between corresponding teeth of successive groups of the face gear teeth, or a multiple of such angle.

8. A differential gearing comprising two sun gears, each having teeth disposed on an end face, rotatably mounted with their axes in line and their toothed faces turned toward one another and spaced apart, a pinion carrier mounted to rotate about the axis of said gears between them, planet pinions rotatably mounted on said carrier with their geometrical axes substantially radial to the before named axis and in a location between the sun gears such that their teeth mesh simultaneously with the teeth of both sun gears; the teeth of said pinions being 'all at the same distance from their respective axes and spaced apart with equal angular spacing, and the teeth of the sun gears having varying spacings such that when one of the sun gears is prevented from rotation while the other is free to rotate, and the pinions are caused to roll about the sun gear axis, a variable speed of rotation is imparted to the free sun gear.

'9. A differential gearing comprising two sun gears, each having teeth disposed on an end face in a plane perpendicular to its axis, rotatably mounted with their axes in line and their toothed faces turned toward one another and spaced apart, a pinion carrier mounted to rotate about the axis of said gears, cylindrical planet pinions rotatably mounted on said carrier with their geometrical axes substantially radial to the before named axis and in a location between the sun gears such that their teeth mesh simultaneously with the teeth of both sun gears; the teeth of said pinions being all at the same distance from their respective axes and spaced apart with equal pitch spacing, and the sun gear teeth being variably spaced with alternate progressive increases and decreases of pitch spacing.

10. A differential gearing comprising two sun gears, each having teeth disposed on an end face in a plane perpendicular to its axis, rotatably mounted with their axes in line and their toothed faces turned toward one another and spaced apart, a pinion carrier mounted to rotate about the axis of said gears, cylindrical planet pinions rotatably mounted on said carrier with their geometrical axes substantially radial to the before named axis and in a location between the sun gears such that their teeth mesh simultaneously with the teeth of both sun gears; the teeth of said pinions being all at the same distance from their respective axes and spaced apart with equal pitch spacing, and the teeth of the sun gears being arranged in a number of groups, in each of which the pitch spacing progressively increases and progressively decreases from one end to the other of the series, all of said teeth being conjugate to the pinion teeth, and the increases and decreases of pitch spacing being alike in all of said series, and the pinions being disposed with an angular spacing around the axis of the sun gears. such that the several pinions are, at any one time, in mesh with corresponding ones of the teeth in the different groups of the sun gears.

11. A difierential gearing comprising two sun gears, each having teeth disposed on an end face with uniform spacing between them on a circle concentric with its axis, said gears being mounted rotatably with their axes in alinement and their toothed faces turned toward one another with a space between them, a pinion carrier mounted to rotate about the axes of said gears, planet pinions supported rotatably by said carrier between and in mesh with the sun gears, the teeth of said planet pinions being equidistant from their respective axes, but spaced unequally around such axes with progressively increasing distances as to a succession of teeth and progresively decreasing distances as to the next following succession of teeth, and all of said pinion teeth being conjugate to the sun gear teeth.

12. A differential gearing comprising sun gears, each having teeth on an end face, mounted coaxially and rotatably with their toothed faces turned toward, and spaced apart from, each other, a planet pinion between and in mesh with both sun gears, and means for revolving said pinion as a driver in an orbit surrounding the sun gear axis; the teeth of sun gears and pinion being relatively unequally spaced with progressively increasing and diminishing spacing such as to cause alternate accelerations and decelerations of one sun gear when the pinion is revolved at uniform speed in its orbit and the other sun gear is withheld from rotation.

JAMES L. WILLIAMSON. 

